The present invention relates generally to the field of machine tools, and, more particularly, to an improved high precision spindle assembly for use in a multi-spindle machine tool (e.g., a screw machine), and to an improved method of forming a precision spindle assembly for such use.
Machine tools exist in a myriad of different forms. Some machine tools, such as screw machines, have multiple spindles that are mounted in a head that is, in turn, rotatably mounted on a body or frame. In some cases, stock-feeding tubes communicate with the spindles, and are arranged to rotate with the head. The rotating head and feed tubes somewhat resembles a Gatling gun. Thus, while the head may be selectively rotated relative to the body or frame, the individual spindles are also arranged to rotate about their respect axes.
In some cases, a screw machine has an outer spindle that is adapted to be mounted on the rotatable head. An inner spindle is operatively arranged within the outer spindle, is keyed for rotational movement therewith, and is arranged to be selectively moved axially relative thereto. A collet is carried on the distal end of the inner spindle. The collet has fingers that are operatively arranged to interact with an inwardly-facing frusto-conical surface provided on the outer spindle. Thus, the inner spindle may be moved in one axial direction relative to the outer spindle to allow the spring-biased collet fingers to move radially away from the spindle axis, or may be moved in the opposite axial direction relative to the outer spindle to cause the collet fingers to move radially inwardly toward the spindle axis, as if to clamp down on a tool positioned in the collet.
It is highly desirable that the frusto-conical surface on the outer spindle assembly be ground so as to be concentric to the rotational axis of the outer spindle, as that outer spindle is actually mounted on the rotatable head. The more coincident the axis of the frusto-conical surface is to the axis of spindle, the more accurate the mounting.
One prior art arrangement of such a spindle is shown and described in U.S. Pat. No. 4,014,558. This patent broadly discloses a chuck-closing mechanism for an automatic screw machine. The patent discloses a single-piece outer spindle and an inner spindle carrying a collet. The fingers of the collet interact with a frusto-conical surface provided on the outer spindle. The inner spindle maybe moved axially within the outer spindle to selectively open and close the collet. The aggregate disclosure of this patent is hereby incorporated by reference with respect to the structure and operation of such a collet.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improved spindle assembly and method of forming same.
In one aspect, the invention provides a spindle assembly (23) that is adapted to be mounted in an opening (22) provided in a rotatable head (20) of a multi-spindle machine tool, such as a Davenport(copyright) multi-spindle screw machine. (Davenport(copyright) is a registered trademark of Davenport Industries, Inc., now Davenport Machine, Inc., 167 Ames Street, Rochester, N.Y. 14611.) The improved spindle assembly broadly comprises: a tubular main spindle part (26) adapted to be inserted into the head opening, and having a first abutment surface (42); a bearing retainer (27) adapted to be threaded into engagement with the head, and having a second abutment surface (55) arranged to face toward the first abutment surface; at least one bearing (28, 28, 28) acting radially between the head and spindle main part, and being arranged between the first and second abutment surfaces; and a retaining nut (29) adapted to be threaded into engagement with the spindle main part so as to form therewith an assembled spindle. The retaining nut has a third abutment surface (83) arranged to bear against the bearing retainer.
In the preferred embodiment, the first and second abutment surfaces are annular. The bearing may be compressed between the first and second abutment surfaces. Each bearing have an inner race (65) and an outer race (66). The first abutment surface (42) is arranged to engage one of the inner and outer races, and the second abutment surface is arranged to engage the other of the inner and outer races. The bearing retainer may have a reversed somewhat C-shaped transverse cross-section. The retaining nut may have a tongue (88) adapted to be inserted into the bearing retainer recess. The retaining nut has a frusto-conical surface (70).
The improved spindle assembly may further include: an inner spindle (49) operatively arranged within the assembled outer spindle, and a multi-fingered collet (51) mounted on one end of the inner spindle. The fingers (52) of the collet engage the frusto-conical surface (70) such that the opening and closing of the collet is determined by the axial position of the inner spindle relative to the assembled spindle. The machine tool may include a frame on which the head is rotatably mounted, first means (e.g., a first motor and associated drive mechanism) for rotating the head relative to the machine frame, and second means (e.g., a second motor and associated drive mechanism) for rotating the assembled spindle assembly relative to the head.
In another aspect, the invention provides a method of forming a spindle assembly, comprising the steps of: providing a body having an opening into which the spindle is to be mounted; providing a tubular main spindle part having a first abutment surface; inserting the main spindle part into the body opening; providing a bearing having an inner race and an outer race; positioning the bearing between the main spindle part and the body; providing a retaining nut having a second abutment surface; mounting the retaining nut on the body so as to compress the bearing between the first and second abutment surfaces; providing a retaining nut; mounting the retaining nut on the main spindle part so as to form therewith an assembled spindle; rotating the assembled spindle relative to the head; and grinding a frusto-conical surface on the retaining nut; thereby to form a frusto-conical surface on the retaining nut that is concentric with the rotational axis defined by the bearing.
This method may include the further steps of: disassembling the assembled spindle from the body; and reassembling the spindle on the head of a machine tool.
Accordingly, the general object of the invention is to provide an improved spindle assembly.
Another object is to provide an improved spindle assembly that is particularly adapted for use with a Davenport multi-spindle machine tool.
Still another object is to provide an improved method of forming a spindle assembly.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings and the appended claims.